The present invention relates generally to an apparatus and method for clamping together and releasing contact lens mold halves for manufacture of contact lenses, and more particularly to an apparatus and method for clamping multiple contact lens mold halves together by way of a single activating source while still providing means to individually adjust the clamping force being supplied to each pair of contact lens mold halves.
It is desirable to directly mold contact lenses rather than form the lenses by machining operations such as lathing. Generally, depositing a predetermined amount of curable substance, such as a polymerizable liquid monomer into a preformed mold cavity forms molded lenses. Thereafter, the liquid monomer is subjected to a curing source such as UV light or heat for a predetermined period of time until the monomer is properly cured. A soft contact lens results when the cured monomer form is separated from the molds and hydrated.
Generally, in the process briefly described above, a large number of contact lens molds are filled with the polymerizable liquid monomer at a station remote from the actual curing apparatus. Herein, the polymerizable liquid monomer is first injected into one (female) half of the mold assembly and then the second (male) half of the assembly is brought into contact with the first half. The opposing surfaces of the mold halves define the optical surface of a contact lens therebetween. The mold halves are lightly clamped together to allow transport from the monomer inject station to the clamping and curing station.
Once the contact lens molds are introduced to the clamping and curing station, it is recognized that problems may occur during the clamping and release procedure generally used in the past. For example, it is recognized that defects may appear in some lenses due to variations caused by providing individual clamping and release mechanisms associated with a respective mold. In previously known systems, the contact lens molds are arranged together in, for example, groups of three. Thereafter, the grouped lens molds are clamped together by individual clamping sources acting on each lens mold. In other words, a separate clamping and release source is provided for each contact lens mold being presented to the curing station. For example, three air cylinders would clamp three molds in a group, respectively, with the three air cylinders being extended and retracted by a common air line. With each group of molds having its own air line, variations were inevitably seen between each air line, and in both the extension and retraction velocities of the cylinders. In this case, each mold or groups of molds may see different clamping and release velocity profiles.
The present invention recognizes the problems that occur in contact lenses molded from a polymerizable material, which are not subjected to uniformly even clamping and release velocity profiles which are being applied to the lens mold halves. Problem areas are seen in improper edge formation, as well as defects in the optical portion of the lenses.
U.S. Pat. No. 5,914,074 to Martin et al entitled xe2x80x9cMold Clamping and Curing of a Polymerizable Hydrogelxe2x80x9d discloses a clamping device for clamping together contact lens mold halves which have a polymerizable material, such as hydrogel, therebetween. The mold halves are clamped together with a predetermined force provided by way of an air cylinder, springs or weights for a predetermined period of time. The mold halves are formed of a material suitable to allow the polymerizable hydrogel material to be exposed to a curing source, such as UV light, to thereby cure the material to a gel-like state. Thereafter, the clamping pressure is removed and the mold halves having the partially cured hydrogel material disposed therebetween is moved to a further station for finish curing.
In addition to the above reference, U.S. Pat. Nos. 3,806,079; 4,284,399; 5,690,473; 5,693,268 and 5,850,107 disclose a liquid monomer clamped in a contact lens mold and polymerized to form a contact lens.
None of the above art solves the problems which occur when using the previously known contact lens clamping methods.
The present invention is directed toward an apparatus for accurately and repeatably clamping together multiple pairs of contact lens mold halves having a polymerizable liquid material contained between each pair. The clamped together contact lens mold halves are thereafter presented to an appropriate source for curing the polymerizable material to form contact lenses.
In this invention, a contact lens mold clamping assembly is presented which with accuracy and repeatability, clamps together and then releases multiple pairs of contact lens mold halves by utilizing a common source for activating the plurality of clamping mechanisms.
The contact lens mold clamping assembly may include a biasing mechanism coupled to each of the plurality of contact lens molds to enable the force being exerted thereon by the clamping assembly to be individually and accurately determined and set.
Further, this invention provides a contact lens mold clamping assembly and a common release mechanism for interaction with the clamping assembly to open the clamping assembly for introduction thereto of assembled contact lens molds, and thereafter releasing the clamps enabling the contact lens molds to be clamped by the clamping assembly. Because each clamp passes through the same, common release mechanism, each clamp sees the same, controlled linear motion profile.